1. Field of the Invention
The present invention relates generally to control valves for controlling flowing fluids and more particularly to control valves for dissipating the energy of high pressure drop flowing fluids.
2. Description of the Background
The high velocity attained by the flowing fluid as it passes through the valve affects the life and application of the control valve. It is known that the damaging effects resulting from the velocity may be reduced by effecting an energy change or conversion of energy in a control valve. Velocity control reduces the erosion of the valve elements by direct impingement of liquid, droplets or foreign matter suspended in the fluid stream. Additional erosion results from cavitation damage which can be reduced by lowered velocity in the valve. Noise generation is a function of velocity raised approximately to the eighth power. Significant noise reduction with little velocity reduction can thus meet any government and industry standards of radiated noise. The problem of quiet operation is of importance in connection with submarines, hospitals or other installations where minimum radiated noise under operating conditions is essential.
The above problems have been widely recognized throughout the valve industry for many years. Attempted solutions have included the conversion of energy of a flowing high pressure drop fluid by subdividing it into a plurality of passageways. Multiple changes in direction provide a tortuous path for the fluid. The result is a pressure drop and velocity control as a function of changes in direction. See, for example, U.S. Pat. No. 3,154,074.
U.S. Pat. No. 3,821,968 discloses a control valve employing cylindrical valve elements. The valve elements are perforated to provide a restriction to fluid flow via a high wetted area to flow area. Resulting flow and fluid friction converts some of the flow energy into heat.
U.S. Pat. No. 3,896,834 discloses a valve for reducing noise resulting from the fluid flow in which the flow controlling valve element is formed as a single helical wound spring, either of the compression or tension type. When the helices are in mutual contact, fluid flow is prevented wherein when the helices are separated in an axial direction, fluid flows through the spaces therebetween.
German Pat. No. 2,316,453 discloses a valve structure having a single conical spring disposed in the flow path between its inlet and outlet. The spring is attached to a valve plug and the reciprocal motion of the plug causes the spring to expand, whereby the space between the convolutions of the spring can be expanded or contracted. When the convolutions of the spring are separated in an axial direction, fluid flow is permitted therethrough.